Vortec 7.4 MPG vs 5.7 on lifted truck

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kylenautique

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Ok, so I fully understand this is a difficult question to answer, but I'm trying to get a gauge on what to expect MPG wise from a 1999 k2500 crew cab short box with a 7.4, 4l80e, 6"lift and 35" tires vs my current 1998 k1500. I don't know what mods the k2500 has, so let's pretend its got a black bear tune and electric fans. My 1998 k1500 has a 5.7, 6" lift, 33" tires, upgraded injector spider, cats removed, black bear tune, 3.73 gears and electric fans.

I have an opportunity to purchase the 1999 k2500, and I just am curious am I going get considerably worst gas MPG, or will they be somewhat close? I drive like a grandpa, and I mainly use my truck as a daily driver, tow rig for a ski boat, family hauler, and running construction materials and firewood to my cabin. Will I vomit at the amount of gas that 7.4 uses, or will I be in the same ball park as my current half ton? If I purchased this new truck, I would tune it with Black Bear and throw electric fans on it to free up as much power as possible and match the shift points to the tires/remove most of TQ management, to help with gas MPG and power.

I'm not expecting to get 20mpg, but will I be under 10 on the highway just driving? What are people getting with these rigs?
 

OutlawDrifter

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Plan on 10 or less, more than likely. Big tires, wind catching lift, basically the world working against you.

My '99 K2500 Suburban on 265/70R17s gets 11.5mpg back and forth to work. Best tank ever was 14mpg @ 68mph. Will run in the low to mid 13s in the low 70mph range. Gets high 11s maybe 12mpg @ 77mph. This is with no cats, BB tune, and better flowing exhaust.

Yes it will be worse than a half ton, but given the choice between a K2500 in a 5.7 or a 7.4...I'll take the big block every day.
 
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